1. Field of the Invention
The present invention generally relates to a fan for cooling an automotive engine. More particularly, the present invention pertains to a valve member of a temperature sensitive fluid fan coupling which has a fan member provided thereon such that the rotation thereof is controllable.
2. Description of the Prior Art
FIG. 3 shows a temperature sensitive fluid fan coupling of the type described above, which has already been proposed by the present inventor in the specification of Japanese Patent Laid-Open No. 60-241534 laid open on Nov. 30, 1985, in which FIG. 3(a) is a sectional view of the fan coupling, and FIG. 3(b) is a front view of a valve member thereof viewed from the front side of the a partition plate. As illustrated, the proposed temperature sensitive fluid fan coupling has a hermetically sealed casing consisting of a casing member 2 and a cover 3. The casing member 2 is supported through a bearing B on a rotary shaft 1 having a driving disk 7 rigidly secured to its distal end. The cover 3 has a cooling fan provided on the outer periphery thereof. The inside of the casing is partitioned by a partition plate 5 into an oil reservoir chamber 6 and a torque transmission chamber 4 which accommodates the driving disk 7, the partition plate 5 having an oil flow regulating bore 5'. The fluid fan coupling further has a dam 12 for controlling the oil when the driving disk 7 is rotating which dam 12 is defined between the peripheral wall portion of the disk 7 and a part of the wall surface of the casing which faces disk 7, and an oil circulating passage 13' which provides communication between the torque transmission chamber 4 and the oil reservoir chamber 6 through the dam 12. In addition, a valve member 8 is provided in the oil reservoir chamber 6 in such a manner as to be activated in respose to the action of a temperature sensitive member (bimetal) 10 caused by a temperature change, the bimetal 10 being provided on the front surface of the cover 3, so that the valve member 8 opens and closes the oil flow regulating bore 5' provided in the partition plate 5 in accordance with a change in the ambient temperature. Thus, the transmission of torque from the driving (rotary shaft) side to the driven side is controlled by varying the effective opening area for flow of oil at the dam 12 defined between the facing wall surfaces of the driving disk 7 and the casing member 2 and at the oil flow regulating bore 5'. Further, a weight 19 is provided either directly or indirectly at the free end of the valve member 8 so that the degree of opening of the oil flow regulating bore 5' is decreased as the speed of rotation of the driven side rises. It should be noted that the reference numeral 1' denotes a flange, 9 a bimetal shaft, 11 a support member, 13 an inlet port, 15 an outlet port, 16 a partition wall, 17, 17' cooling fins, and 18, 18' fan securing bolt holes.
The valve member having the above-described arrangement enables elimination of the discontinuous change in the speed of rotation of the fan, that is, the problem that the rotation speed of the fan may change abruptly despite no change in temperature in the case where the degree of opening of the oil feed port is controlled by the displacement of the bimetal only. However, there are still some cases where the above-described problem cannot be sufficiently overcome simply by providing a weight on the valve member.